A problem with the fabrication of two stage amplifiers, such as a two state operational amplifier (Op Amp) is that the process can vary significantly over process corners. This causes the common-mode voltage of the first stage to reduce the operating range of the second stage, which can even cause the second state to drop out of the saturation region.
Previous two gain state Op Amps either use one common-mode feedback circuit, or two common-mode feedback circuits that set the common-mode voltage for both stages. This results in the same common-mode voltage for the first and second stages.